When a substantially closed space is used for the placement of a relatively large amount of electronic devices such as computer hardware and/or equipment used for telecom applications, it is often referred to as a data centre.
Electronic devices usually comprise a heat source and are known to generate a relatively large amount of heat. If no appropriate measures are taken, the temperature in the space can rise to such a level that it may cause the devices to malfunction, to operate outside normal specifications, or reduce device lifetime. Thus measures need to be taken to keep at least the temperature in the space within a certain desired bandwidth, preferably at a constant level. Comparable requirements may apply for the air humidity.
Normally, the temperature inside the space is controlled by venting cool air into the space and extract the by the heat sources, e.g. electronic devices, heated air from the space for cooling, after which the cooled air is vented into the space again. The air inside the space is circulated in this manner along a first recirculation path.
The circulated air can be cooled by a relatively complex active cooling device like a compression based cooling device using a medium to transfer heat from one place to another. Such active cooling devices use a relatively large amount of energy. Further, these devices are generally not very efficient and possible leaks in the active cooling devices may cause environmental hazards depending on the medium that is used.
As an alternative, an air-to-air heat exchanger in the form of a thermal recovery wheel can be used, wherein heat is transferred from an air flow inside the space via the thermal recovery wheel to a second air flow outside the space. The use of the thermal recovery wheel is based on the insight that the temperature of the second air flow outside the space (an environment) is often low enough to cool the space to a desired temperature. In this manner, no active high-energy consuming cooling device is required for cooling.
The thermal recovery wheel is a slowly rotating wheel with an open structure that is placed partially in an air flow circulating in the space, and partially in an air flow circulating in the environment of the space. Heat is transferred from the air flow in the space to the thermal recovery wheel and subsequently to the air flow in the environment after rotation of the wheel.
The environment can be open air, but it can also be a space other than the space that has to be cooled. Preferably, the environment is a space that is substantially separated from the space that has to be cooled and is preferably large enough so that transferring a relatively large amount of heat to the environment will not cause the environment to change its temperature in such a way that the environment can not cool the space anymore.
However, a main disadvantage of the solution with the thermal recovery wheel is that air can leak through gaps between the thermal recovery wheel and the wall separating the two air flows and that the thermal recovery wheel by itself transports air from the environment to inside the space and vice versa. This makes the cooling process less effective.
The leakage and/or exchange of air in the heat exchanger may also have consequences for the fire safety installation. Normally a fire safety installation is used that reduces the oxygen level in the space to prevent a fire from starting or to extinguish the fire. When air leaks and/or is exchanged through the heat exchanger, this fire safety installation has to be bigger to compensate for the leakage and/or exchange of air or is not able to properly extinguish the fire.
The impact of wind on the façade where an air inlet and outlet to the environment are situated, may greatly increase the size of the mentioned negative effects. Similarly, these negative effects may increase during operation due to wear of the rotating thermal recovery wheel.